The invention relates to a method of manufacturing a reflecting mirror from a stainless steel sheet as a base material, and more particularly to a method of manufacturing a reflecting mirror having a double nickel layer plated on the surface of the stainless steel sheet.
A metallic reflecting mirror which employs aluminium as a base material is known since old. The mirror is formed by electropolishing the aluminium surface to make it lustrous, and forming a transparent oxide film thereon to provide a corrosion resistance and abrasion resistance. Such mirror can be manufactured in a number of processes using different electrolytes or electrolytic steps, but almost all of these processes employ an alkaline electrolyte, so that any impurity such as iron or copper in the base material is left on the surface thereof without being precipitated into the electrolyte. As a result, the base material must be a high purity aluminium in excess of 99.97%. Still, it is difficult to obtain a uniformly bright surface, and the soft nature of the base material involves the essential disadvantage of being vulnerable to damage, which renders it inadequate for industrial purposes which require a working of the product into a desired configuration or size.
There has been some attempt to manufacture a reflecting mirror from a stainless steel sheet as a base material, a view of the workability and strength which it affords. However, the prior proposal has been a mere buffing of the surface of the stainless steel sheet, and the resulting product had a poor brightness and also exhibited a substantial amount of distortion of image, which prevented it practical use except for the merit of inexpensiveness. Since the success of removing the passivity of the surface of stainless steel, techniques have been proposed to a plate a variety of metals on its surface. By way of example, after the pre-treatment, a bright nickel layer can be plated onto the surface of the stainless steel, using a standard Watts bath or Weisberg bath. However, the resulting plated layer exhibited a blackish tint which reflects the tone of the base material, and thus was wanting in brightness. In addition, with the proposed techniques, the pre-treatment included an electrocleaning of the steel surface and an activation by a cathodic treatment in sulfuric or hydrochloric acid. The activation resulted in a reduced adherence of a nickel layer which is subsequently plated, and thus the plated layer is susceptible to exfoliation during the working of the product, particularly when it is bent into a given configuration.
Therefore, it is an object of the invention to provide a method of manufacturing an inexpensive reflecting mirror having a bright mirror surface which exhibits a high gloss and is free from distortion of image.
It is another object of the invention to provide a method of manufacturing a reflecting mirror having a double nickel layer plated on the surface of a stainless steel sheet and having a close adherence thereto, thus enhancing the workability.
It is a further object of the invention to provide a method of manufacturing a reflecting mirror from a stainless steel sheet as a base material, which can be reduced to practice with a simple apparatus.